MLA

Steinberg, Saul, 1914-1999. Betty Parsons Gallery. Box 5, folder 90-91. 1948-1983, undated. https://collections.library.yale.edu/catalog/10034232.

APA, 6th edition

Steinberg, Saul, 1914-1999. (["Box 5, folder 90-91"])(1948-1983, undated)[Betty Parsons Gallery]. https://collections.library.yale.edu/catalog/10034232.